1. Field of the Invention
The present invention relates to a solid-state imaging apparatus having a solid-state imaging device and a signal processing circuit, used in a video camera and the like and a method for driving the solid-state imaging device.
2. Description of the Related Art
Recently, solid-state imaging devices and signal processing circuits used for such solid-state imaging devices has been improved in performance and are in use in a video camera for consumer use.
A conventional solid-state imaging device and a signal processing circuit used for such a solid-state imaging device described in Japanese Laid-Open Patent Publication No. 2-87685 will be described with reference to FIG. 18.
Such a conventional solid-state imaging device includes photoelectric converting sections arranged two dimensionally and a vertical charge transfer section for vertically transferring charges which are output by the photoelectric converting sections. A plurality of reading operations are performed within a period in which images corresponding to one image plane are formed, and the charges which are output are mixed in the vertical charge transfer section. The vertical charge transfer section outputs the result.
For example, the two reading operations are performed within the above-described period. A charge Q1 read in the first reading operation is accumulated in time duration t1, and a charge Q2 read in the second reading operation is accumulated in time duration t2, which is different from time duration t1. FIG. 18 illustrates the photoelectric converting characteristic of the conventional solid-state imaging device. In FIG. 18, the vertical axis represents the intensity of light, and the horizontal axis represents the level of the voltage obtained by converting the quantity of the output charge. The solid line indicates such a characteristic of the charge Q1, and the dashed line indicates such a characteristic of the charge Q2. The chain line represents such a characteristic of a charge Q3 obtained as a result of the mixture of the charges Q1 and Q2. As is illustrated in FIG. 18, the voltage based on the charge Q1 which is output in the first reading operation reaches a saturation level of the photoelectric converting section when the intensity of light becomes B. The voltage based on the charge Q2 which is output in the second reading operation reaches a saturation level of the photoelectric converting section when the intensity of light becomes D. The charge Q2 provides a wide dynamic range, but provides a low S/N ratio when the intensity of light is low due to the low signal level thereof. The charge Q1 provides a narrow dynamic range, but provides a high S/N ratio due to the high signal level thereof. Thus, the charge Q3 provides a wide dynamic range and a high S/N ratio even if the intensity of light is low.
A solid-state imaging apparatus having the above-described structure has drawbacks. Specifically, the saturation levels of the photoelectric converting sections corresponding to different pixels are not uniform. Thus, the knee point of the charge Q3 at which the curve representing the photoelectric converting characteristic turns drastically is different among different pixels. Such non-uniformity is represented as noise having a fixed pattern in an area of a video image having a high luminance, which significantly deteriorates the quality of the image.
Moreover, in the case where a plurality of color filters having different spectroscopic characteristics are provided in order to display a color image by a single solid-state imaging apparatus, color separation cannot be done due to the photoelectric converting characteristic having a knee point.